Conventionally, it has been known to share data files existing in a server with a plurality of parties. This can be done by, for example, uploading data files to a server through a network and personal computers connected to the server are allowed to access to those data files. However, re-uploading a data file to the server becomes necessary in the event that the data file once uploaded to the server is accidentally deleted. Generally, re-loading the data file is troublesome because the data file may not be retained in a client device from which the data file is uploaded.